Dozens of angry locals have held a demonstration in southern Afghanistan after a rocket exploded at a wedding, killing at least 20 people and injuring more than 50.

Many of the victims in the December 31 tragedy in Helmand Province's Sangin district were women and children.

Officials have launched an investigation into whether the rocket was fired from an Afghan Army checkpoint near the house where the wedding was being celebrated.

Officials said they were looking into whether the rocket was fired in an exchange with Taliban militants or whether it was fired arbitrarily.

A spokesman for the provincial government told RFE/RL's Radio Free Afghanistan that a delegation has been dispatched to find out "what caused the incident and its circumstances."

An unidentified resident of Sangin told Radio Free Afghanistan on January 1 that rockets struck his home, killing at least 10 members of his family.

"My kids have been killed and injured. My sisters have been killed. My aunts have been killed," he said. "At least 10 to 15 members of my family have been killed or injured. Overall, around 40 people have been killed, including guests and family members. "

Sangin is located in the poppy-producing region of the Helmand River valley and has seen fierce fighting between government forces and Taliban fighters over the last six months.

Afghanistan assumed full responsibility for security on January 1 after NATO-led coalition forces formally ended their combat mission a day earlier.

The move will provide a stern test for the 350,000-strong Afghan security forces that will bear responsibility for fighting the Taliban.

Around 13,000 foreign troops, mostly Americans, will remain in the country under a new two-year mission named Resolute Support to train Afghan troops.

In a speech on January 1 to mark the handover, President Ashraf Ghani congratulated the country because "Afghan forces are now able to take full security responsibility in protecting their country's soil and sovereignty."

At least 3,188 Afghan civilians were killed in the intensifying war with Taliban insurgents in 2014, making it the deadliest year on record for noncombatants, the United Nations said in a report last week.